Tissue electrodes implanted in a body of a subject for electrical pacing, defibrillation, or cardioversion of a heart are known. More specifically, tissue electrodes implanted within, on, or about the heart have been used to reverse (i.e., defibrillate or cardiovert) certain life threatening arrhythmias (i.e., irregular heart rhythms), or to stimulate contraction (i.e., pacing) of the heart, where electrical energy is applied to the heart via the tissue electrodes to return the heart to normal rhythm. Tissue electrodes have also been used to sense cardiac activity, such as intrinsic or responsive signals of the heart. Tissue electrodes detect abnormally slow (referred to as “bradyarrhythmia”) or abnormally fast (referred to as “tachyarrhythmia”) heartbeats. In response to the sensed bradyarrhythmia or tachyarrhythmia condition, a cardiac sensor/stimulator device produces pacing or defibrillation pulses, respectively, to correct the condition.
The tissue electrodes' ability to sense, pace, defibrillate or cardiovert a subject's heart depends, in part, on the location of the electrodes within, on, or about the heart and the interface between the tissue electrodes and nearby heart tissue. Typically, the tissue electrodes are arranged on a lead body in two ways (or categories)—bipolar and unipolar arrangements. First, a bipolar arrangement includes a pair of tissue electrodes on the lead which form a single electrical circuit (i.e., one electrode is positive and one electrode is negative). Second, a unipolar arrangement includes one tissue electrode which represents one pole, while the other pole is represented by the cardiac sensor/stimulator device body or minute ventilation electrode. Through the use of unipolar and bipolar configured leads, the sensing, pacing, defibrillation or cardioversion is limited, sometimes to a heart location other than or different from the desired or optimum position.
Some subjects may require a sensing/stimulation system to detect and pace or shock an abnormal heart in more than one location in the cardiac region, wherein such locations are distant from one another. In such situations, the only solutions currently available are for a subject to have multiple individual leads or a lead with multiple lead proximal end portions (referred to as “legs”) implanted within his/her thoracic cavity or elsewhere, one of the leads/legs for use in sensing activity or delivering stimulation to a first position and one or more other leads/legs for use in sensing activity or delivering stimulation to at least a second position.
Having multiple individual leads or having a lead with multiple lead proximal end portions implanted within the subject's thoracic cavity or elsewhere is undesirable for many reasons. For instance, the complexity and time involved in implanting multiple leads/legs is typically greater than the complexity and time needed to implant a single lead having one lead proximal end portion. In addition, multiple leads or lead legs may mechanically interact with one another after implantation in a negative fashion. As another example, as more leads are implanted within, on, or about the heart, the ability to add other leads is reduced. Similarly, as more lead legs are connected to a cardiac sensor/stimulator device, the device header must grow to accommodate the additional lead connector cavities. A further issue related to the implantation of multiple leads or lead legs is increased pocket bulk (i.e., more space/volume in the body(s) of implanted hardware).
Another problem of current leads, systems, and methods relates to the treatment of cardiovascular subjects experiencing congestive heart failure (referred to simply as “CHF”). CHF, which can result from a number of causes such as long-term hypertension, is a condition in which the muscle in the walls of at least one of the right and (more typically) the left side of the heart deteriorates resulting in, among other things, disynchronous heart rhythm and enlarging of the heart. Often times in subjects experiencing CHF, the left side of the heart does not beat at the same time as the right side causing the pumping action of the heart to be inefficient. Further, subjects experiencing CHF often develop enlarged hearts as a result of scarring or formation of deposits in the heart muscle. For reasons similar to those discussed above, currently available leads, systems, and methods may not provide the sensing, pacing, defibrillation or cardioversion that is needed to adequately or optimally treat CHF.